1. Field of the Invention
This invention relates to an X-ray tomograph using a computer (hereinafter referred to as "an X-ray-operated CT apparatus", when applicable); and more particularly to an X-ray-operated CT apparatus having a data processing function adapted to correct the difference in sensitivity of the different channels of a multi-channel X-ray detector unit.
2. Discussion of Prior Art
In an X-ray-operated CT apparatus, as shown in FIG. 1, an X-ray tube 1 and a multi-channel X-ray detector unit 2 are revolved around the axis of revolution 0 to thus revolve around an object or body 3 under examination. X-ray transmission data of body 3 are collected so that the image of a plane section of the body is formed by an image reconstructing unit 4 and is displayed by a display unit 5. Due to the sensitivity difference of the different channels of multi-channel X-ray detector unit 2, a concentric-circle-like pattern called an "artefact" is formed in the plane section image. In order to eliminate the artefact in the conventional X-ray-operated CT apparatus, a calibrating test body having a predetermined configuration is used or the body 3 under examination is removed from the apparatus. X-ray transmission data are then collected to form sensitivity correcting data which are used in the formation of the plane section image. In particular, the sensitivity correcting data are used to correct the errors in the X-ray transmission data of body 3 which are caused by the sensitivity difference of the different channels of multi-channel X-ray detector unit 2.
However, in the above-described method, the dose and photon energy of X-rays in an X-ray-operated CT apparatus change with time. For instance, the dose and photon energy of X-rays change as the resistance (or temperature) of the filament or the characteristics of the target of X-ray tube 1 vary with time. In addition, the temperature characteristics or electrical characteristics of the different channels of multi-channel X-ray detector unit 2 change with time.
Since the dose and photon energy of X-rays in an X-ray-operated CT apparataus change as described above, the different channels of the multi-channel X-ray detector unit become different in the dose and photon energy of X-rays with respect to one another. Therefore, no uniformity is established between the collection of sensitivity correcting data and the collection of X-ray transmission data. Accordingly, the sensitivity difference mentioned above can not be accurately corrected, and therefore it is difficult to completely eliminate artefacts. In this regard, the conventional X-ray-operated CT apparatus is not advantageous.